1. Field of the Invention
The invention relates to portable gyroscopic compass devices of the kind adapted for surveying purposes and more particularly relates to portable north-seeking gyroscopic surveying devices including means for rapidly aligning the apparatus with respect to geographic north.
2. Description of the Prior Art
Prior art gyrocompass devices useful in north-seeking systems for surveying applications generally fall into two classes: (1) those which are physically combined with a theodolite so that there is direct mechanical means for transfer of the north reference to the theodolite azimuth circle and (2) those which are physically separate from the theodolite so other means must be provided for the transfer of the azimuth reference information. Typical of the former devices are the devices presented in the W. G. Wing U.S. Pat. Nos. 4,033,045, issued July 5, 1977 for a "Portable Surveying Gyrocompass Apparatus", and 4,109,391, issued Aug. 29, 1978 for a "Portable Surveying Compass With Flux Valve and Gyrocompass Alignment Modes", both assigned to Sperry Corporation. Also of general interest is the sensitive element system disclosed in the T. R. Quermann U.S. Patent Application Ser. No. 67,842, filed Aug. 20, 1979 for a "Gyroscope Indexing Drive Mechanism" and assigned to Sperry Corporation; this mechanism appears in a north seeker designed for operation apart from a theodolite.
Three problems arise with integrated systems of the class (1) kind. Inspection of the aforementioned Wing patents, for example, shows that a standard, off-the-shelf theodolite cannot be used in the integrated device. Incorporation of the gyroscopic sensitive element within a theodolite requires significant revision of the latter, and vice versa. Accordingly, it is apparent that a procedure using a directly purchasable theodolite has evident advantages.
The class (1) instrumentation has further problems when in operation. Clearly, the theodolite must be undisturbed throughout the north-finding operation. As a consequence, the time used in making a first survey operation at a representative station is the sum of the time needed to set up the instruments, the actual north-finding time, and the time used for actual theodolite sightings and readings. Since the steps are taken in sequence, the total time can be significant. Furthermore, it is normally the practice to operate the theodolite on a relatively high tripod, but such a configuration can result in significant wind-induced disturbances which would undesirably reduce the accuracy of any north finder mounted on the theodolite.
In the instance of class (2) systems, the prior art is known to have used optical transfer methods, but has never provided a convenient means of alignment of the theodolite with respect to the north seeker. The prior art systems are not practical unless two operators are available, one of whom will be unnecessary in the remainder of the operation at a selected station.